Happily, here's one from Delta as I described above https://i.imgur.com/wwYQXy1.png. Sadly (for me, at least), I've never flown above "First" on such a configuration from Delta though :). Like you had noted, they call it 4 cabin classes... but the economy classes ("Main" & "Comfort") are both treated as a single cabin in terms of service and the difference in economy seats is an inch or two of leg room. So it's really a 3 cabin of: business, first, economy.
Again, hbosch said ATL<->SFO... and you aren't going to be flying Air France or Japan Airlines for that route. My list, as far as I'm aware, was exhaustive for that route. It was not a cherry picked search of airlines which do it that way or global claim of what all other airlines do, only a response to the particular claim. On other routes/airlines the statement could, or rather "would", certainly have been true. Honestly, I think those airlines have it the right way around, but, having flown the exact route and the same airlines internationally, it did not match my experience for the route - which agreed with the labeling for all airlines for that route according to the links above. Unless, perhaps I'm missing that American or similar does actually have a ATL<->SFO to be compared with?
It literally says "first" in the upper right hand corner of the image indicating the red seats, which are clearly not as nice as the purple seats, aka Delta One?
That is a composite image, with screenshots from two different pages (and I'm virtually certain from two different flights), not a legend of the seating chart and a seating chart.
I can't find an ATL-SFO flight offering Premium Select and in fact couldn't find a domestic Premium Select flight at all, but on flights where I can find Premium Select, such as BOS-AMS on May 10, 2026, here is the fare selection screenshot from that flight, and the seating chart screenshot, including the legend on a single page:
Notably, neither of those use red for "First Class" and there's no confusion between trying to use a legend from one page/flight as a key to understand a seating chart on a different page/flight. In fact, they both use red for "Premium Select" and booking Premium Select on that flight gives you a fare class of "A", which is specific to Premium Select (and NOT to First Class/Delta One, which share J, C, D, I, and Z, because Delta One is just a branding of First Class, rather than a cabin distinct from first class).
Again, hbosch said ATL<->SFO... and you aren't going to be flying Air France or Japan Airlines for that route. My list, as far as I'm aware, was exhaustive for that route. It was not a cherry picked search of airlines which do it that way or global claim of what all other airlines do, only a response to the particular claim. On other routes/airlines the statement could, or rather "would", certainly have been true. Honestly, I think those airlines have it the right way around, but, having flown the exact route and the same airlines internationally, it did not match my experience for the route - which agreed with the labeling for all airlines for that route according to the links above. Unless, perhaps I'm missing that American or similar does actually have a ATL<->SFO to be compared with?